540
FXUS63 KDLH 261128
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
628 AM CDT Sat Jul 26 2025

.KEY MESSAGES...

- A hot and humid weekend with heat indices in the 90s today and
  Sunday. A Heat Advisory is in effect for today. A Extreme
  Heat Watch was issued for Sunday.

- There are plenty of chances for periods of storms starting
  this morning and ending Monday morning. The most widespread
  and intense thunderstorms will occur Sunday afternoon into
  Sunday night. There is a 15 to 25 percent chance of flash
  flooding with large hail and damaging wind also possible.

- Less humid and slightly cooler Tuesday through the end of next
  week.

&&

.DISCUSSION...
Issued at 404 AM CDT Sat Jul 26 2025

The main story for today will be the elevated heat and
humidity. A Heat Advisory is in effect for nearly all of the
Northland from noon until 8 PM Saturday. High temperatures are
forecast to reach the mid to upper 80s, but high humidity will
lead to heat index values climbing into the low 90s.

Before the heat sets in, a cluster of thunderstorms currently
over the NW MN is expected to cross north-central Minnesota
after 6 AM though will be weakening as they move eastward.
Outflow boundaries from these storms could trigger afternoon
convection. MLCAPE values of 15002500J/kg with weak deep-layer
shear of 2530 knots will limit storm organization, favoring
pulse storms. The primary threats with these storms will be
brief heavy downpours and hail up to half-dollar size and a
microburst threat.

The heat and humidity persist into Sunday, with another warm
day on tap. Highs will range from the low 80s in the north to
the low 90s in the south. This will result in widespread heat
index values from the upper 80s to the upper 90s, with a few
locations in the St. Croix Valley potentially touching the low
100s. An Extreme Heat Watch has been issued.

A slow-moving cold front will sag into the region on Sunday,
providing the necessary low-level convergence to initiate
thunderstorm development in the very unstable air mass. MLCAPE
values are forecast to climb into the 20003000J/kg range ahead
of the front. Wind shear will be decent for storm organization
with 40-50kt of 0-6km bulk shear, suggesting more organized
storms are expected. The primary threats will be damaging hail,
damaging downburst winds, and torrential rainfall. The Storm
Prediction Center (SPC) has placed the area under a Marginal
Risk for severe thunderstorms while the WPC has us under a
Slight Risk for excessive rainfall. The rainfall threat is legit
with precipitable water values forecast to surge to 1.5 to 2.0
inches. As a nocturnal low-level jet develops Sunday night,
moisture transport will become more efficient, with winds
oriented nearly parallel to the frontal boundary. This setup
strongly favors the development of training thunderstorms
leading to a significant flood risk. Given the saturated soils
from heavy rainfall over the past week, a Flood Watch may be
required for parts of the area. For now, will let the scene play
out a bit as confidence in location and timing is still a bit
too uncertain to make a watch decision.

Storms should gradually weaken and exit the region early Monday
morning. The extended forecast period from Tuesday through
Friday looks to feature a significant pattern change. A mid-
level ridge is expected to shift westward, allowing for a cooler
and drier northwest flow aloft to settle over the region. This
will bring a period of quieter weather, though the northerly
trajectory will probably bring a return of smoke from Canadian
wildfires. :(

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 624 AM CDT Sat Jul 26 2025

One round of showers and tstorms fizzles as it crosses this
morning, after which should be a VFR day. Tonight some fog with
another MCS bringing showers and tstorms by morning. Fairly
light southwesterly winds though gusty to 15-18kt in the
afternoon.

&&

.MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/...
Issued at 404 AM CDT Sat Jul 26 2025

Main concerns for western Lake Superior over the next several
days will be a few thunderstorm chances this afternoon and
Sunday night through early Monday morning. A few storms may be
strong. Winds away from storms will be less than 15 knots and
generally from the SW.

For the open water discussion, refer to the NWS Marquette Area
Forecast Discussion at weather.gov/mqt.

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
MN...Heat Advisory from noon today to 8 PM CDT this evening for
     MNZ010>012-018-019-025-026-033>038.
     Extreme Heat Watch Sunday afternoon for MNZ036>038.
WI...Heat Advisory from noon today to 8 PM CDT this evening for
     WIZ001>003-006>008.
     Extreme Heat Watch Sunday afternoon for WIZ001>004-006>009.
MARINE...None.

&&

$$

DISCUSSION...Wolfe
AVIATION...Wolfe
MARINE...Wolfe